Glossy paper

ABSTRACT

The invention concerns a glossy or scintillating paper provided with a roughness more than 30 ml/mm measured in accordance with the ISO 8791-2 standard, entirely manufactured on a paper machine, and characterized in that it comprises reflecting microplates or microbeads of dimensions less than 300μ incorporating at least one optically transparent material in their structure.

The invention relates to the field of glossy or scintillating papers that can be used for producing magazines, brochures, publicity documents, art papers or printing and writing papers.

Glossy papers are generally obtained by means of an operation of calendering or supercalendering papers coated with an essentially inorganic coating, said calendering operation enabling the surface to be thoroughly smoothed.

Gloss is obtained on the coated calendered paper by uniform reflection of light on the extremely smooth and uniform surface.

This manner of proceeding has been known for many years as well as the constraints inherent in this type of production of which a few known disadvantages are mentioned below:

-   -   the paper has to be coated or contains a very high level of         filler so that the physical calendering operation is effective,         which requires a costly operation if it is carried out off the         paper production line, or an economically unfavorable operation         if it is produced on the machine, by reason of productivity         losses caused by the processing device. Such a coated paper has         significantly inferior physical properties compared with an         uncoated paper, particularly as regards rigidity, burst strength         etc.     -   the paper has to be calendered or supercalendered, that is to         say the surface is smoothed by a rolling operation. The         operation also induces a loss of the mechanical properties of         the paper and brings about a paper with a “mineral” feel, very         different from soft agreeable papers such as those sold in         ranges of art papers or covers.     -   a calendering operation as previously described must, in order         to lead to a uniform gloss, be carried out on a paper that is         very uniform, both in its surface appearance as well as in its         thickness, in order to prevent the formation of a hammered         appearance. Papermakers refer to a lookthrough characteristic         that is as high as possible.

Apart from the preceding problems, the method does not make it possible in any way to obtain a textured or embossed paper since the method consists of leveling the surface completely.

Such embossed papers correspond, non-exclusively, to papers of printing or writing categories, for texts and covers and art papers, for which a special paper texture is often sought. Paper texture should be understood to mean papers having watermarks, special lookthroughs, laid lines and various markings such as those produced with grained felts or marking presses etc.

Another means to enable glossy papers to be produced and more particularly papers with embossing consists of coating with a gloss varnish during a converting operation, off the paper machine. Gloss is obtained by depositing large quantities of a glossy polymer.

A method similar to that of varnishing can be carried out on a coating machine with a formula close to that of a varnish.

This manner of proceeding with texture papers requires, in all cases, a supplementary operation and the application of a thick layer of a glossy binder, which is not always technically achievable according to the amount of embossing of the paper.

This type of varnishing treatment or coating has been known for a long time and also the disadvantages associated with excess costs.

Another technique consists of laminating the finished paper with a polymer film.

The laminating operation carried out off the machine, when the paper is produced, is also costly and corresponds to a different application from that of the invention, which corresponds rather to the field of conversion of printed paper than to that of production.

Colored papers present on the market are rarely sold with a gloss effect since the fact of coating these papers modifies the color and leads to non-uniform effects which do not encourage sales, while varnishing that involves a supplementary operation leads to a prohibitive excess cost, and moreover machines producing these papers do not generally possess a coating device on a production line and are therefore generally not suitable for producing a deposit of glossy coating in the same operation as that of paper production, and in fact these papers are not very widespread. There therefore exists a need for producing glossy colored papers, whether textured or not, that can be produced in an economical manner.

The object of the invention is therefore to resolve these main difficulties, that is to say to produce a glossy or scintillating paper in an economical manner without a calendering or varnishing operation on all paper machines, with or without an integrated coating machine, and with all achievable bases, in particular colored or textured ones.

The glossy or scintillating paper according to the invention has a roughness greater that 30 ml/min measured in accordance with ISO 8791-2 standard and is produced entirely on a paper machine and is characterized in that it includes reflecting microplatelets or microbeads with a size less than 300 μm incorporating at least one optically transparent material in their structure.

The advantages of the paper according to the invention are economical, since it is possible to produce a glossy or scintillating paper without forming calendering, coating or conversion, and the same time technical, since glossy papers such as those proposed make it possible to obtain special optical effects and in particular remarkable gloss on textured or colored papers with integral retention of the mechanical properties of the paper, in particular as concerns rigidity and burst strength.

Another noteworthy effect of the invention, not produced by known calendered coated or varnished papers is that the optical yield of the paper according to the invention is variable according to the ambient illumination at the moment of observation. When illumination is high, in the sense of light reaching the paper, treatment leads to a uniform gloss effect, whereas when illumination is low individual scintillating points are perceptible on the surface of said paper.

Another advantage obtained by the treatment composition is that the glossy or scintillated paper retains all its physical mechanical properties as well as its appearance and feel properties, which is a determining factor in the case of textured papers for which a relief effect is required and for which an agreeable feel is often required, and this is particularly the case for papers incorporating cotton linters in their fibrous composition. Coating compositions followed by calendering or varnishing bring about a loss of these appearance properties that are particularly appreciated for art papers and most papers used in printing and writing.

Taking into account the previously mentioned advantages and on account of the fact that the treatment is applicable over a large number of different substrates for various novel products, not existing on the market, can be produced, in particular in a non limiting manner:

-   -   Glossy or scintillating or colored textured papers.     -   Glossy or scintillating embossed papers suitable for inkjet         printing with a reinforced quality according to the teachings of         patent application FR 0313700.     -   Glossy or scintillating watermarked papers suitable for inkjet         printing with a reinforced quality according to the teachings of         patent application FR 0313700, for example papers that can be         used as letterheads, mailings or even as security papers.     -   Glossy or scintillating art papers, such as papers for         watercolor, drawing, pastels etc, possessing the usual         properties of texture and feel.

Other features and advantages of the invention will become apparent from the following description and the non-limiting examples provided.

In this description and within the meaning of the invention, coated papers should be understood to mean any papers having at their surface a coating containing at least one polymeric binder and possibly mineral or organic fillers, the operation being carried out on or off the paper machine by means of a coating device enabling the deposited layer to be kept on the surface of the paper, that is to say the layer does not penetrate more than 20% and generally less than 10% into the paper thickness.

An uncoated paper should be understood to mean a base paper having no surface treatment or impregnation or coating by means of various devices, preferably rollers, which cause the treatment composition to penetrate into all the thickness of the sheet or at least 30% of said thickness.

Within the meaning of this description, a varnished paper is a paper on which a glossy transparent layer is deposited, penetrating very little into the paper, that is to say less than 20% of its thickness, generally consisting substantially of a glossy polymer without additional fillers and with a dry matter deposit at least equal to 2 g/m² and preferably more than 5 g/m². The varnishing operation is carried out off the paper machine on specific equipment, a varnishing machine, or by means of a coating apparatus.

The gloss or scintillation of the paper within the meaning of the invention is defined by the visual effect produced on observing the paper at a variable angle between 20° and 80°. According to the quantity and nature of the treatment composition applied, the optical effect produced is situated between a scintillating effect, such as that produced by snow in the sun, that is to say randomly distributed bright points reflecting light, and a gloss effect without individual scintillating points.

The optical effects obtained in the invention are not only variable according to the angle of observation of the treated paper but also according to the ambient illumination, and the visual effect changes according to whether the lighting is low, when under these conditions individual scintillating points are more particularly visible, or high, and under these conditions the gloss effect is uniform and very intense. These effects are very different from those obtained with calendered coated or varnished papers which never exhibit a scintillating appearance and of which the gloss is relatively independent of the illuminating conditions.

The roughness of the paper is usually measured by means of various apparatuses such as “Bekk”, “Bendtsen” or “Sheffield” apparatuses, said roughness measurement being standardized, and reference is made here more particularly to ISO 8791-2 standard making it possible to express the roughness of the paper in ml/min with the “Bendtsen” apparatus. Papers according to the invention have a roughness of at least 30 ml/min and preferably more than 100 ml/min, which in the traditional classification of papers corresponds to untreated or slightly calendered papers but in no way to traditional glossy papers of which the roughness values measured by Bendtsen are situated at values less than 30 ml/min and more generally less than 10 ml/min.

Textured papers for which the treatment has special interest have roughnesses greater than 300 ml/min and generally above 1000 ml/min when texturing is employed by means of marking felts or engraved presses.

The treatment composition according to the invention is applicable on all types of papers, in particular textured or colored papers, by means of a device positioned inside the paper machine, preferably a size press, a device with multiple rollers known under the names “gate roll” or “Massey”, an impregnator, a device with rollers depositing pre-metered amounts for the coating formulation such as that called for example a “blade metering size press” (“BMSP”), or any other device comprising at least one roller in contact with the paper.

Traditional coating devices positioned inside the paper machine can be used, such as for example trailing blade or bar coaters.

The treatment composition according to the invention employs reflecting particles in the form of platelets or microbeads incorporating in their structure at least one optically transparent material, generally a component classified in the general family of glasses, for example a borosilicate.

The size of the particles, that is to say their greatest length in the case of microplatelets or the diameter in the case of microbeads, is less than 300 μm and preferably between 50 and 250 μm, so that the reflecting effect is optimal. Particles that are too fine, namely of the size of the usual coating pigments, typically less than 30 μm, penetrate too far into the paper base during application of the treatment composition and their gloss or scintillating effect is very attenuated.

The reflecting effect of platelets or beads is created by the association of an optically transparent material and a material reflecting light. Production of these particles in the form of platelets or beads is known and is carried out in particular by Merck who have developed technologies enabling particles to be obtained with different materials in successive layers.

The products employed within the context of the invention are noteworthy in that they can be used at extremely low doses over all types of substrates and more particularly on substrates having considerable roughness such as previously defined, and in that they are applicable by conventional means present on all paper machines and not only by coating devices.

Preferably, according to the invention, the roughness of the finished paper is greater than 100 ml/min in accordance with ISO 8791-2 standard and the reflecting microplatelets or microbeads are incorporated at a rate of at least 0.05%, preferably at least 0.15% by dry weight based on the finished paper.

The treatment composition according to the invention comprises at least one category of particles in the form of microplatelets or microbeads incorporating at least one optically transparent material in their structure, and at least one binder enabling said particles to be fixed in the paper and on its surface. Reflecting microplatelets, with a size between 20 and 200 μm, which are entirely suitable, are marketed by Merck under the name Miraval® and under the reference 5411 Magic White.

The binder can conventionally be a starch, a polyvinyl alcohol, a latex or any other polymer that can be used in a known manner in papermaking. The quantity and nature of said binder is chosen according to the coating means employed and factors related to the subsequent use of the paper such as for example the printing means employed.

Preferably, at least one binder is used that brings about gloss and is optically transparent so as not to cause a deterioration in the effect obtained with the particles incorporated. Such binders that can reinforce the gloss of reflecting particles are for example, and in a non-limiting manner, polymers chosen from the family of polyvinyl alcohols, acrylic latices and polyvinylpyrrolidones.

According to the invention, the glossy or scintillating paper that has reflecting microplatelets or microbeads at a rate of at least 0.05% and preferably at least 0.15% dry weight based on the paper, also contains a polymeric binder at a rate of at least 0.1% and preferably more than 1% dry weight based on the paper weight.

So as to retain the reflecting microplatelets or microbeads in the paper, the level of binder inside the treatment composition should be sufficiently high, and it has been found particularly advantageous to add at least the same quantity of binder, by dry weight incorporated, as the reflecting particles, and preferably at least twice more.

The invention also relates to the method for obtaining a glossy or scintillating paper with a roughness greater than 30 ml/min measured in accordance with ISO 8791-2 standard, produced on a paper machine in a single step, and characterized by the following successive steps:

-   -   producing a substrate paper,     -   coating said substrate with a treatment composition comprising         reflecting microplatelets or microbeads with a size less than         300 μm incorporating at least one optically transparent material         in their structure, and containing at least one polymeric binder         in a dry quantity at least equal to that of said microplatelets         or said microbeads,     -   drying said composition and reeling the finished paper.

Preferably, the method is characterized by the fact that the substrate paper can be colored, textured, watermarked, laid, marked with felts or engraved presses or any other device known to give embossing or non-uniformity to the paper by any method inside the paper machine, before the treatment formulation is applied to its surface.

The method for obtaining a glossy or scintillating paper is also characterized in that the reflecting microplatelets or microbeads are incorporated in the paper at the same time as the polymeric binder in a treatment composition applied by means of a coating device comprising at least one roller, in the conventional manner of a size press.

The method is particularly well suited to obtaining glossy or scintillating colored papers without a calendering or coating operation.

EXAMPLE 1

According to an advantageous embodiment of the invention, a treatment composition containing reflecting microplatelets incorporating at least one optically transparent material in their structure, was applied with a size press onto 150 g/m² paper textured by means of marker felts.

The treatment composition consisted of a solution comprising by weight based on the total weight of the formulation: 2% of a high-viscosity polyvinyl alcohol, Mowiol® 28-99 marketed by Seppic and 0.5% Miraval® 5411 Magic White from Merck.

The pick-up of the preceding solution at the size press was 35% by weight based on the paper, which represented a weight of microplatelets incorporated in the paper of 0.175% and a weight of polymeric binder of 0.7%. Said binder was in a quantity four times greater than the quantity of reflecting microplatelets in the composition.

The gloss effect obtained varied according to the illuminating conditions. When the paper was observed in sunlight or close to a lamp, the gloss effect was uniform and very intense. When the paper was observed in a place with low illumination, essentially scintillating points were observed.

The glossy white paper obtained in this way had a roughness measured in accordance with ISO 8791-2 standard, of 1500 ml/min.

The mechanical properties of the paper, particularly its rigidity and burst strength, were identical to those of a glossy untreated paper.

EXAMPLE 2

According to another example, a glossy laid paper was obtained by producing a colored 100 g/m² paper laid on the paper machine table and body-colored in a conventional way.

The colored and textured sheet was coated on the size press with a composition comprising by weight, based on the total weight of the formulation: 1% of a high-viscosity polyvinyl alcohol, Mowiol® 28-99 marketed by Seppic, 5% by dry weight of a styrene butadiene latex DL 955 marketed by Dow Chemical and 2% of Miraval® 5411 Magic White from Merck.

The treatment composition penetrated through the entire thickness of the paper and a pick-up of 40% was found. On account of the fact that the reflecting microplatelets were incorporated at a rate of 0.8% by dry weight based on the paper weight, the polymeric binder represented by polyvinyl alcohol and latex was incorporated at a rate of three times the quantity of reflecting microplatelets and at a rate of 2.4% based on the paper weight.

The finished paper still retained its original color and texture before treatment, roughness was measured at 1000 ml/min, and the gloss of the paper was very strong under high illumination producing a particular optical yield but with conventional properties of feel and relief produced by laid lines.

The mechanical properties of such a paper, in particular its rigidity and burst strength, were identical to those of a glossy untreated paper.

EXAMPLE 3

A glossy paper with a Bendtsen roughness measured as 800 ml/min, suitable for inkjet printing with a reinforced quality such as defined in patent FR 0313700, comprising:

-   -   A white textured base paper of 250 g/m² was made by producing a         base containing a fibrous composition of 100% cotton linters, in         which there was inserted, by weight based on the fibers, 15% of         Tixolex® 28 from Rhodia, 1% by weight of cationic starch, 3% as         a commercial product of a binding agent Aquapel® 305 from         Hercules and 3% of calcium carbonate used as an additional         filler. The preceding composition was deposited on the wire of a         cylinder mold of a paper machine, pressed with a device with         engraved presses to give the texture of a paper for watercolor         and then dried in the usual manner until the end of pre-drying         where a treatment composition was coated on the size press.     -   A treatment composition comprising, by weight of commercial         products based on the total weight of solutions: 6% cationic PVA         CM 318 from Kuraray, 10% Tixosil® 365SP with 22% dry matter from         Rhodia and 3% reflecting microplatelets Miraval® 5411 Magic         White from Merck.

The preceding solution was applied by means of a size press on the base paper at the rate of at least 30 liters of treatment composition for 100 kg of paper, which took account of the fact that this paper represented approximately 30% of the treated thickness and a quantity of hydrophilic binder of 1.8% based on the paper weight. The reflecting microplatelets were incorporated at a rate of 0.9% in dry product based on the finished paper.

The paper coated in this way was dried on a drying unit and the finished product was reeled without calendering so as to preserve the texture formed by the engraved presses. The product possessed the texture of paper for watercolor with a high gloss and a high ability to be printed by inkjet.

The mechanical properties of such a paper, in particular its rigidity and burst strength, were identical to those of a glossy untreated paper.

Such a paper could be used for the reproduction of works of art on inkjet printers with wide formats or as a base for the printing of photos in office printers. The equivalent does not exist on the market of such a paper that is at the same time textured, glossy and suitable for inkjet printing, even produced by a different technique.

In the method claimed, the fibers used to produce a paper can be cellulosic and/or cotton linters, all or in part, in association or not with synthetic fibers or other natural fibers. All additives traditionally used in papermaking such as additional fillers (talc, kaolin, calcium carbonate etc), binding agents, retention agents, coloring agents, optical brighteners, etc. can be employed without departing from the scope of the invention.

The texture of the product can be strong or non-existent, the paper can be watermarked or not, it can be with a high or low grammage without departing from the scope of the invention which is to provide a glossy effect to uncalendered and unvarnished papers, while preserving their usual appearance properties, in particular roughness and feel.

Apart from those already mentioned, one of the advantages of the invention is that it is possible to produce a paper that is treated differently on its two sides, directly in the papermaking process, and finally to obtain in this way a paper having two different glosses on its two faces, which represents a considerable commercial advantage. For example, a paper can be produced marked with a marker felt on one face and a smooth surface on the opposite face, or in a more sophisticated manner, two different textures on the two faces by combining various marker felts and/or associated engraved presses with an identical treatment on the two faces at the size press.

It can also be envisaged to obtain different optical effects on the two faces by means of a symmetrical base paper coated differently on these two sides, for example by combining a size press treatment and a coating on one face on the paper machine, or a treatment at the size press with different solutions on its two faces. A great variety of products can be obtained in this way.

According to the invention, it is possible to treat all types of paper base, which means that very special papers, such as those aimed at making the paper suitable for inkjet printing, are included, and in particular products resulting from techniques described in the Applicant's unpublished application FR 0313700. According to the combination of the two inventions, it is possible to obtain an inkjet printing paper with a reinforced quality, and moreover gloss, directly on a paper machine. Tests of papers combining the teaching of application FR 0313700 and of the present invention show that a glossy paper with a reinforced inkjet quality can be achieved and that this paper leads to a printed sheet of which the printed part appears to an observer as “metallized”, this effect being completely novel and remarkable, especially if a textured base is employed.

Several variants are also possible for the treatment composition aimed at obtaining a glossy paper, and various additives can in particular be added, such as cobinders, flow modifying agents, antifoam agents, antifungal agents, optical brighteners, coloring agents and various other compounds traditionally known in papermaking, without departing from the scope of the invention.

Various means for applying the treatment composition can be envisaged in order to give various effects, and it is for example possible to imagine treating only part of the paper sheet in order to produce glossy strips neighboring and alternating with strips of untreated paper. It is also possible to envisage applying the treatment composition by spraying or by any coating means, whether conventional or not, inside the paper machine, without departing from the scope of the invention.

The invention is of course not limited to the embodiments described and represented as examples, but it also comprises all equivalent techniques as well as combinations thereof. 

1. A glossy or scintillating paper with a roughness greater than 30 ml/min measured in accordance with ISO 8791-2 standard, produced entirely on a paper machine, said paper including reflecting microplatelets or microbeads with size less than 300 μm incorporating at least one optically transparent material in their structure.
 2. The glossy or scintillating paper as claimed in claim 1, wherein the roughness is greater than 100 ml/min in accordance with ISO 8791-2 standard and the reflecting microplatelets or microbeads are incorporated at a rate of at least 0.05%, preferably at least 0.15% by dry weight based on the finished paper.
 3. The glossy or scintillating paper as claimed in claim 1, obtained by coating with a treatment composition containing reflecting microplatelets or microbeads as well as at least one polymeric binder, which treatment composition enables said microplatelets or microbeads to be incorporated at a rate of at least 0.05% and preferably at least 0.15% by dry weight based on the finished paper, as well as said polymeric binder at a rate of at least 0.1% and preferably more than 1% by dry weight based on the paper weight.
 4. The glossy or scintillating paper as claimed in claim 3, obtained by coating with a treatment composition containing a dry binder weight at least equal to the weight of reflecting microplatelets or microbeads.
 5. The glossy or scintillating paper as claimed in claim 4, wherein the binder employed is chosen from the family of polyvinyl alcohols, acrylic latices or polyvinylpyrrolidones.
 6. The glossy or scintillating paper as claimed in claim 3, wherein the treatment composition is coated by means of equipment possessing at least one roller, for example of the size press, “Massey”, “gate-roll” or “BMSP” type.
 7. The glossy or scintillating paper as claimed in claim 3, and which can be colored, textured, watermarked, laid, marked with felts or engraved presses, so as to give embossing or non-uniformity to the paper inside the paper machine, before the treatment formulation is applied to its surface.
 8. A method for obtaining a glossy or scintillating paper with a roughness greater than 30 ml/min measured in accordance with ISO 8791-2 standard, produced on a paper machine in a single step, characterized by the following successive steps: producing a substrate paper, coating said substrate with a treatment composition comprising reflecting microplatelets or microbeads with a size less than 300 μm incorporating at least one optically transparent material in their structure, and containing at least one polymeric binder in a dry quantity at least equal to that of said microplatelets or said microbeads, drying said composition and reeling the finished paper.
 9. The method for obtaining a glossy or scintillating paper as claimed in claim 8, wherein the substrate can be colored, textured, watermarked, laid, marked with felts or engraved presses, so as to give embossing or non-uniformity to the paper inside the paper machine, before the treatment formulation is applied to its surface.
 10. The method for obtaining a glossy or scintillating paper as claimed in claim 8, wherein the treatment composition is applied by means of a coating device possessing at least one roller, for example of the size press, “Massey”, “gate-roll” or “BMSP” type, making it possible to incorporate in the paper a quantity of at least 0.05% and preferably at least 0.15% by dry weight of said microplatelets or microbeads based on the finished paper, as well as at least one polymeric binder at a rate of at least 0.5% and preferably more than 1% by dry weight based on the paper weight. 